The invention refers to the devices for dividing a continuous web of wrapping material into successive single sections of a same length, particularly for dividing a web of wrapping material into successive single bands used in the manufacture of filter-tipped cigarettes, which device comprises a rotary cutting roller with one or more angularly equispaced peripheral radial blades, the cutting edge of which is parallel to the axis of the shaft for driving in rotation the said cutting roller, and a rotary counter-roller having one or more peripheral anvils that cooperate each with one blade on the cutting roller, and which is possibly provided with suction ports for holding onto the counter-roller the single sections cut from the web fed around the counter-roller.
In these devices, the cutting of the web is effected by parting it off, that is to say, the web is simultaneously engaged over its entire width by the cutting edge of each blade on the cutting roller, and by one blow it is cut off against the respective anvil on the counter-roller. The cadenced blows of the cutting roller blades on on the counter-roller anvils produce noise and vibrations.
To obviate to this inconveniences, devices of the above disclosed type have been proposed, in which the blades are not fixedly secured to the cutting roller, but are so mounted as to be radially slidable thereon between lateral guide walls, and as to be urged radially outward as far as an abutment stop member by return helical or cup springs which allow an elastic retraction of each blade when the blade hits against the associated anvil, in order to reduce the noise and dampen the vibrations. This solution however presents some other inconveniences. In fact, so-called fretting phenomena occur, that is to say, abrasion or corrosion phenomena due to friction, which affect above all the springs and in a short time annihilate their efficiency. To replace the springs with special elastomers is not the best solution of the problem, since these materials although being capable to maintain their elastic properties at the high temperatures produced by the deformation work, allow only small elastic retractions of the blades. Moreover, the slidable embodiment of the blades involves a considerably complicated construction, while the tobacco dust may penetrate between the guide surfaces, whereby the sliding of the blades is made difficult.
A further inconvenience of the known cutting devices of the above disclosed types resides in a quick and irregular wear of the blade cutting edges due to any inevitable inexactness in positioning the blades with respect to the associated anvils on the counter-roller. In fact, each blade generally hits against the associated anvil at first with one end and then with the entire length of its cutting edge, which will be very soon the cause of defective cuts. To obviate such an inconvenience, it is known to use blades which are tiltable in radial planes passing through the axis of the cutting roller. At the same time, each blade is elastically loaded in the longitudinal direction by means of elements sliding along both sides of the blade.
The said sides of the blade are oblique sides which converge in the outward direction, and at the first cut the elastic load acting thereupon puts the blade straight, so that it is definitely arranged when its cutting edge is not initially parallel to the surface of the respective anvil. The construction of these devices however is a very complicated one.